In a supercharged combustion engine, a certain amount of leakage of fully or partly combusted exhaust gases always occur between the piston rings and the cylinder wall to the crankcase during the compression steps of the combustion engine. This exhaust gas leakage is generally referred to as blow-by, even though the gases also contain condensate from the engine oil in the crankcase. To prevent unfiltered exhaust gases from being discharged directly to the environment, these exhaust gases are ventilated to the intake system of the engine for combustion in the cylinders. This principle is generally referred to as PCV, Positive Crankcase Ventilation.
The blow-by gases are supplied directly from the crankcase, via a hose or the like, to the inlet in the air duct between the turbo compressor and the air filter. Alternatively, the exhaust gases are first supplied to the cylinder head cover (which is in fluid communication with the crankcase via the transmission between the crankshaft and the camshaft(s)). The underpressure that prevails upstream the compressor provide for this blow-by gas ventilation.
During driving situations when the engine works hard, a powerful suction is created upstream the compressor. To avoid a too large underpressure in the crankcase, which can result in an increased blow-by, a throttle element is arranged in the hose.
It forms a flow resistance in the hose which can be adapted for adjusting the evacuated amounts of exhaust gases as desired.
One example of this known PCV-principle is shown in FIG. 1, which schematically depicts a multi-cylinder combustion engine 1 of type Otto. The cylinders 3 of the engine are provided with not shown exhaust gas valves, leading the exhaust gases to a exhaust gas collector 5 which is shared in common by the cylinders. The engine is adapted for supercharging by means of an exhaust gas driven turbo compressor having a turbine 7 and a compressor 9 driven by the turbine 7. The turbine is supplied from the exhaust gas collector 5 and is in fluid communication, via an exhaust gas duct 11, with a conventional catalytic converter 13 and one or several not shown sound absorbers. The inlet 15 of the compressor is connected to an air filter 17 arranged upstream for filtering the charged air that is supplied to the compressor. The outlet of the compressor is connected to a cooler 19 for cooling the compressed charged air before it is further supplied to the cylinders 3 of the engine.
The combustion engine is provided with a PCV-device 21 (shown with dashed lines), which is intended to ventilate the exhaust gases from the crankcase. A throttle element 23 is arranged in the PCV-device and serves to control the amount of blow-by gases that are ventilated from the crankcase. During the operation of the engine, the underpressure that prevails just upstream the compressor will draw air from the environment via the air filter 17, but also from the crankcase via the PCV-device 21. In driving situations when the compressor 9 works hard (and thus creates a more powerful suction just upstream the compressor), the throttle element 23 will provide an efficient flow resistance in the PCV-device 21 preventing the pressure from decreasing too much in the crank case, which could result in an increased blow-by. During wintertime driving, or during other cold conditions, condensate is easily formed in the crankcase which can be transformed into ice. A particular critical place is as mentioned before the throttle element 23 in the PCV-device 21.
However, during some driving conditions the water content in the blow-by gases creates large amounts of condensation water, e.g. during wintertime or during frequent starts and stops of the engine. This formation of condensate can cause great problems if freezed to ice. A particularly critical place is the throttle element in the hose, and since an underpressure prevails, ice may also be formed at temperatures of several degrees above zero. Besides that the crankcase ventilation can be blocked by an ice plug leading to drainage of engine oil, the ice plug may also when it finally melts loose the grip and join the blow-by gas flow into the compressor, which can lead to damages of the compressor wheel.